The ruling triggered a variety of reactions and exposed Americans' mindset after September 11, 2001.
"This must be looked in a larger context of the war on terrorism. If he gets the death penalty, then he becomes a martyr, a symbol to rally more of the radical Muslims," said Charles Wolf, whose wife was killed in the attack.
"Are we playing right into their hands if we give him the death penalty? Do we make ourselves weaker? Are we going to let ourselves be manipulated into killing him? Because, why else would he have come out and said 'I did this, this and that'?"
"I don't want to play into his hands, I want to be smarter than that," Wolf told AFP.
Lorie Van Auken, a New Jersey widow, disagreed with the jury's decision at a federal courthouse in Alexandria, Virginia.
Jury will now have to decide if
Moussaoui should be executed
"I don't think he contributed to what happened on September 11. I think he's been scapegoated," she said.
Van Auken questioned the reasoning behind the jury's decision, which accepted the prosecution's argument that the Frenchman was responsible for the 2001 attacks, because he withheld information from authorities that could have prevented them.
"I didn't know that to withhold information made you eligible for the death penalty ... the CIA withheld information from the FBI," she said.
Patty Casazza, another victim's relative from New Jersey, also pointed out that federal officials had withheld information that could have foiled the plot.
"If we had had their information, the FBI might have been able to stop the plot. But that didn't happen," said Casazza, who also lost her husband in the attacks.
"I'd rather see someone with direct ties to 9/11 receive the death penalty, like Osama bin Laden, but, of course, we haven't caught him," she added.
Outside the Alexandria courtroom, relatives were divided over the decision that ended three and a half weeks of the first phase of the trial.
"It's very emotional ... it's hard to describe. I thought I would be delighted, but I wasn't. I still feel sorry for him"
Abraham Scott, a victim's husband
"The jury did a long, good job," said Rosemary Dillard, whose husband Eddy was killed in the attacks that the Frenchman admitted plotting.
"We couldn't have a better closing, for all of us, even those who don't believe in death penalty. We know he is guilty," she said.
Abraham Scott, whose wife Janice died when a hijacked plane was flown into the Pentagon in Washington, struggled to express his feelings.
"It's very emotional ... it's hard to describe. I thought I would be delighted, but I wasn't. I still feel sorry for him," he said.
"I don't think Moussaoui is totally to blame, even though I think he deserves death. I equally blame the government," he said in a choked voice.
Now the jury must decide whether Moussaoui should be executed, by lethal injection.
"I don't see why they would do otherwise," Scott said.